1. Field of the Invention
The present invention relates to a process for producing a semiconductor device, and particularly an improvement of a process in which the edges of a window through a glass film of the semiconductor device are smoothed or rounded so as to prevent the disconnection of wiring of the semiconductor device at such edges.
2. Description of the Prior Art
It has been proposed by Intel Corporation, in Japanese published patent application No. 50-6143, that the edges of a glass layer formed on an insulating layer, which covers a semiconductor substrate, be smoothed or rounded by the following procedure. After exposing pertinent portions of the semiconductor substrate, the glass film is heated so that the edges of a window are formed smoothly by a plastic flow, and electrical contact with the exposed part of the semiconductor substrate is provided through the smoothed window. It is possible by means of this proposed process to smooth or round the edges formed at the shoulder part of a window through a glass layer, for example, the phosphosilicate glass (PSG) layer of an N channel MIS type semiconductor device, in which the N type source and drain regions are formed on the P type semiconductor substrate. In the production of such an N channel MIS type semiconductor device, when a layer of an electrode metal, for example aluminum, is to be located on the source and drain regions, the phosphosilicate glass (PSG) is thermally melted so as to smooth the edges of the window, thereby preventing the disconnection of the electrode at the edges. However, when the melting treatment as proposed in the Japanese published patent application No. 50-6143 is applied to the P channel MIS type semiconductor device, the phosphorus is deposited from the PSG layer during the melting thereof and forms a phosphorus diffusion layer on the surface of the P type source and drain regions, which can result in poor contact or contact resistance between the electrode metal and these regions. Furthermore, in the production of the N channel MIS type semiconductor device, the phosphorus is disadvantageously diffused from the PSG layer into the N type source and drain regions in which, prior to the heating of the PSG layer, the impurities already deposited determines the junction depth and resistance of the source and drain regions.
It is an object of the present invention to provide a simple process for achieving the prevention of an inferior connection of electrodes with a substrate at an electrode window and to prevent the diffusion of impurities from a glass layer to a semiconductor substrate.
It is another object of the present invention to provide a simple process for preventing inadequate contact between a metal layer of electrodes and the source and drain regions of a P channel MIS type semiconductor device.
It is a further object of the present invention to provide a process in which hydrogen can be used in the improvement and stabilization of interface conditions between a semiconductor substrate and a gate insulating film, in combination with the measures for preventing inadequate contact between a metal layer of electrodes and the source and drain regions of a P channel MIS type semiconductor device.
In accordance with the present invention, there is provided a process for producing a semiconductor device comprising,
a semiconductor substrate, on which a source region and a drain region are formed with a gate region positioned between the source and drain regions, PA1 a gate insulating film formed on the gate region, and, PA1 a gate electrode formed on the gate insulating film, said process comprising the steps of: PA1 a semiconductor substrate, PA1 an insulating film formed on one region of the semiconductor substrate, and PA1 an electrode formed on the insulating film, said process comprising the steps of: PA1 forming the insulating film; PA1 forming the electrode on the insulating film; PA1 forming a masking film over the electrode; PA1 forming a glass layer over the masking film; PA1 opening a precursory electrode window through a predetermined portion of the glass layer; PA1 subjecting the glass layer to a heat treatment; PA1 opening an aperture at the precursory window through the masking film, thereby completing an electrode window; PA1 depositing an electrode material on the so completed window, thereby placing on the window an electrode, which electrode extends therefrom; and PA1 subjecting the semiconductor substrate to a heat treatment under a hydrogen atmosphere subsequent to the heat treatment step of the glass layer and prior to the depositing step of the electrode material.
forming the gate insulating film; PA2 forming the gate electrode on the gate insulating film; PA2 forming the source and drain regions in such a manner that the gate electrode is positioned between these regions; PA2 forming a masking film over the source and drain regions and gate electrode; PA2 forming a glass layer over the masking film; PA2 opening precursory electrode windows through predetermined portions of the glass layer; PA2 subjecting the glass layer to a heat treatment; PA2 opening an aperture at the precursory windows through said masking film, thereby completing electrode windows; PA2 depositing an electrode material on the so completed electrode windows, which electrode material extends from the windows; and PA2 subjecting the semiconductor substrate to a heat treatment under a hydrogen atmosphere subsequently to the heat treatment step of the glass layer and prior to the step of depositing the electrode material.
In accordance with the present invention, there is also provided a process for producing a semiconductor device, such as an MOS capacitor, comprising,
One of the important points of the present invention resides in the fact that the masking film, which inhibits impurity penetration, is formed over at least the electrode covering an insulating layer and occasionally over the source, drain and gate regions, prior to the formation of the glass layer, and further, that the semiconductor substrate is subjected to a heat treatment under a hydrogen atmosphere subsequent to the heating step of the glass layer and prior to the depositing step of the electrode material.
In the process of the present invention, the masking film inhibits diffusion of impurities of the glass layer, such as arsenic silicate glass, borosilicate glass and especially phosphosilicate glass (PSG), into the semiconductor substrate. The penetration of phosphorus from the PSG into the P type regions of the semiconductor substrate can advantageously be inhibited by the masking film. The masking film may be one layer of silicon nitride film, but preferably should be two layers consisting of a lower silicon dioxide film and an upper silicon nitride film. One of the functions of the lower silicon dioxide film is to protect the semiconductor substrate from etching during the etching of the upper silicon nitride film. When the silicon nitride film is subjected to a plasma etching by means of, for example, carbon tetrafluoride gas, if the silicon dioxide film has a thickness ranging from 200 to 300 A, it can effectively interrupt the effects of the Freon gas. Another function of the lower silicon dioxide film is to inhibit the penetration of the precipitated phosphorus in the PSG film into the semiconductor substrate. The silicon dioxide film may be produced by a known thermal oxidation method of the silicon substrate and has a thickness preferably in the range of from 200 to 300 A. The silicon nitride film may be produced by a known chemical vapour deposition method using ammonia and monosilane, and has a thickness preferably in the range of from 400 to 500 A.
Another important point of the present invention is that the silicon nitride film, on which the glass layer is deposited, is not removed selectively. It is, therefore, possible to produce an MIS type semiconductor device by a simple process without an inconvenient step of selective removal of the silicon nitride film. The heat treatment under the hydrogen atmosphere according to the present invention can be carried out equally effectively at any point in the production of a semiconductor, i.e. after the melting of the glass layer and before the depositing of the electrode material. When the heat treatment under the hydrogen atmosphere is carried out at an elevated temperature of 800.degree. C. or higher, in addition to a known heat treatment under a hydrogen atmosphere at a low temperature of from 400.degree. to 500.degree. C., the surface state of the semiconductor substrate, especially the interface state between the semiconductor substrate and gate oxide film, is considerably improved over the known heat treatment under hydrogen. The heating time at the high and low temperatures mentioned above ranges from 20 to 60 minutes. According to the process of the present invention, secular changes of properties of the semiconductor device can be reduced to a level lower than that obtained by the conventional process.